EFFECT OF GAMMA-RADIATION ON MAJOR AROMA COMPOUNDS AND VANILLIN GLUCOSIDE OF CURED VANILLA BEANS (VANILLA PLANIFOLIA)
Radiation processing of food materials by gamma-radiation is a well-established method for microbial decontamination and insect disinfestation. Irradiation of spices at doses ranging from 10 to 30 kGy has been reported to result in complete elimination of microorganisms with negligible changes in the flavour quality. The effect of gamma-radiation on microflora and vanillin content of cured vanilla beans in the dose range of 5 - 50 kGy has been investigated, but its effect on other major aroma compounds and vanillin glucoside (vanillin aroma precursor) remaining after curing have not been studied so far. Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one such compound used as a flavouring agent and as a dietary component. It is the major component of natural vanilla, which is one of the most widely used and important flavouring materials throughout the world. Vanillin is an antioxidant capable of protecting membrane against lipid peroxidation and DNA against strand breaks induced by reactive oxygen species. The present work was aimed to study the effect of gamma-radiation processing on the major aroma compounds of cured vanilla beans and also to investigate possible enhancement in vanillin content by the radiolytic breakdown of vanillin glucoside present already. Cured vanilla beans were irradiated (5, 10, 15, 20 and 30 kGy) and the vanillin content of control and irradiated samples were analysed, respectively for possible enhancement of vanillin content by radiolysis of vanillin glucoside. Radiolytic breakdown of glycosidic precursors of aroma constituents and consequent release of free aroma was shown to result in the enhancement of aroma quality of these products. Since a considerable amount of vanillin exists as its glycosidic precursor in cured vanilla pods, a possible enhancement in yield of vanillin by radiation processing is thus expected. Hence the highly stable oxygen–carbon linkage between vanillin and glucose limits the possible enhancement of aroma quality of irradiated beans.